A rolling bearing generally includes an inner ring, an outer ring, a rolling element, and a retainer. An open end thereof may be provided with a sealing member in order to prevent the intrusion of foreign substances from the outside or the leakage of the lubricant enclosed inside. The lubrication inside the bearing is carried out by the lubricant such as oil or grease, and various devises have been made in order to improve the lubricating characteristic of the bearing.
For example, Patent Document 1 has suggested the technique of improving the lubricating characteristic by forming a lubricating film on a retainer. Patent Document 1 describes a rolling device whose outer member, inner member, rolling element, and the like have their surface provided with a predetermined lubricating film. The lubricating film is formed of a solid lubricant through a shot peening process and is used for preventing the smearing, burning, abrasion, and peeling under the high speed and large load (see Patent Document 1). Moreover, Patent Document 2 has suggested the technique of improving the lubricating characteristic by changing the lubricant, the lubricating condition, and the like. Patent Document 2 describes the grease composition used for a bearing, which contains predetermined ester oil and diurea compound in a predetermined mixing amount. This can achieve the excellent resistance against the separation and the grease leakage, and suppress the early burning even in the use for the bearing of the outer ring rotation (see Patent Document 2).
Another technique of improving the lubricating characteristic by changing the shape of the retainer is disclosed in Patent Document 3. Patent Document 3 describes a deep groove ball bearing including a retainer, which includes two annular holding plates formed by pressing a steel plate and which is provided with a polygonal pocket part. This can reduce the rotational torque of the bearing (see Patent Document 3).
Moreover, copiers and printers often employ a rolling bearing for rotatably supporting the rotatable components such as a sheet feeding roller, a photosensitive drum, and a fixing roller. It has been known that if the bearing is charged, the photosensitive part to which the toner is attached is adversely influenced and the image quality will be deteriorated. The grounding mechanism has been typically used to prevent the charging but considering that the grounding mechanism is complicated and the smaller space for the device main body is desired, it is desirable that the rolling bearing has the function of preventing the charging.
Typically, Patent Documents 4 to 6 have suggested the rolling bearing that enables the electric conduction between the inner and outer rings in the bearing for preventing the charging. Patent Document 4 describes the rolling bearing that enables the conduction between the inner and outer rings by attaching a conductive thin wire to a steel plate shield of the bearing and bringing the thin wire in contact with the inner ring groove. This bearing allows the electric conduction for a long time regardless of the number of rotations and prevents the noise, and Patent Document 4 suggests a plurality of modes in regard to how the thin wire is attached and what kind of shape the sealing member has. Patent Document 5 describes the bearing including the contact type sealing member, and since the sealing member has the conductivity, the electric conduction between the inner and outer rings is possible.
Patent Document 6 describes the rolling bearing having the conductive grease enclosed in the bearing. This bearing employs the conductive material such as carbon black as the thickener of the grease, thereby allowing the electric conduction between the inner and outer rings through the conductive grease during the rotation.